Certain embodiments of the present invention generally relate to a screw for securing surfaces together. More particularly, certain embodiments of the present invention relate to a load cell that secures a heat sink to electronic components.
Many electronic components with electrical contacts mating with each other are used in applications in which controlled load forces press against the electronic components. Typically the electronic components are secured to other components, such as a heat sink, by a fastening device that delivers a load force against the electronic component and the heat sink that facilitates mating between contacts. If too much load force is applied to the electronic components, the components may fracture. However, if too little load force is applied to the electronic components, the electrical contacts may form a weak electrical connection. In order to deliver an appropriate load force, a load cell is used to secure an electronic component to a heat sink.
A typical load cell for use with electronic components is described in U.S. Pat. No. 6,196,849 and No. 6,164,980 issued to Goodwin. The load cells of the ""849 and ""980 patents include a shoulder screw, a compression spring, and a washer. The screw includes a screw head, a shaft, a threaded body, and a barb. The barb extends circumferentially around the shaft under the head of the screw. At least one turn of the spring is positioned between the screw head and the barb with the spring suspended along the shaft and the threaded body of the screw. Connectable electronic components such as a bolster plate, electronic socket, and a heat sink all have threaded apertures that are aligned with each other, so the threaded body of the screw may be inserted into the aligned threaded apertures and secure the electronic components to each other. The washer is unattached to the load cell and may be positioned on the shaft below the spring when the threaded body of the screw is rotatably inserted into the threaded apertures. The spring is compressed as the threaded body is rotatably inserted, and the washer prevents the compressed spring from damaging component surfaces. The spring size and screw length correspond to each other in such a way that, when the spring is fully compressed, a fixed length of the threaded body is inside, and secures, the electronic components as the spring applies a controlled load along the load cell to the electronic components.
The typical load cell suffers from a number of drawbacks. First, the load cell utilizes a standard washer that has a large tolerance. The larger the tolerance for a washer, the greater the compression of the spring relative to the length of the screw. Hence, large washer tolerances cause a range of large loads to be applied to electronic components that may damage such components.
Secondly, securing electronic components to each other with the load cell is time consuming and difficult. The washer is first placed around the threaded aperture on the heat sink surface, and then the screw is rotatably inserted into the threaded aperture until the spring is compressed between the screw head and the washer. This two-step process is further complicated when the heat sink includes a standoff and/or fins situated around the threaded aperture.
Thus a need exists for a load cell that is easy to install and that provides better loading control.
Certain embodiments provide a load cell for securing a first structure to a second structure with a desired amount of force. The load cell includes a screw that has a body with a threaded portion along a first end and a head along a second end opposed to the first end. The load cell also includes a spring that is received over the body, having a first end and a second end opposite one another configured to exert a desired amount of force when the spring is compressed. The load cell further includes a spring retention member. The spring retention member includes an opening therethrough that receives the body of the screw. The spring retention member has a bushing secured to at least one of the spring and the body and a washer extending outward from the bushing. The first end and the second end of the spring press against the washer and the head, respectively.
Certain embodiments provide a load cell for threadably joining a heat sink to a second structure with a desired amount of force. The load cell includes a screw that has a body with a threaded portion along a first end and a head along a second end opposed to the first end. The load cell also includes a spring that is received over the body, having a first end and a second end opposite one another configured to exert a desired amount of force when the spring is compressed. The load cell further includes a spring retention member. The spring retention member includes an opening therethrough that receives the body of the screw. The spring retention member has a bushing secured to at least one of the spring and the body and a washer extending outward from the bushing. The first end and the second end of the spring press against the washer and the head, respectively. The load cell also includes a heat sink that has a base and heat dissipating fins. The base includes threaded openings therethrough that are configured to secure the heat sink to an electronic component.